1. Field of the Invention
This invention relates to a novel ball valve constructed so that in the opening and closing actions of a ball, a valve seat retainer is displaced to allow a valve seat to disengage itself from the peripheral surface of the ball.
2. Description of the Prior Art
Generally ball valves are of the construction illustrated in FIG. 1 of the accompanying drawings. Thus, an annular valve seat retainer 3 is accommodated in a fluid passageway 2 of a valve housing 1 in such a manner that such retainer 3 may be displaced both in an upstream and a downstream direction and an annular valve seat 4 supported by the valve seat retainer 3 abuts the peripheral surface of a ball 5 to establish a fluid-tight seal therebetween. In the above-noted arrangement, the valve seat 4 abuts in its entirety the periphery of the ball 5 in the fully opened and closed positions of the body but such is not the case in intermediate stages of rotation of the ball 5. Thus, partway between the fully closed and fully opened positions, a portion of the valve seat 4 is disengaged from the ball 5 to face an opening 6 bored through the ball 5. In this manner, while a part of the valve seat 4 is always in contact with the periphery of the ball 5, such is not true with the remaining part of the valve seat 4, and since these two parts are worn or damaged in dissimilar degrees due to their differential conditions of engagement with the peripheral surface of the ball 5, leakage of fluid can occur in the region as the valve is operated for a protracted time. Furthermore, because during the rotation of the ball 5, its peripheral surface is always urged against at least a part of the valve seat 4, the rotation of the ball 5 requires a large torque and, particularly where the valve seat 4 is constructed of rubber or other material having high coefficient of static friction, requires an actuator with a large output for the opening and closing operation of the ball 5.